1. Field of the Invention
The present invention relates to silicon carbide refractories suitable for preparing large size blocks having a low porosity and a high strength, a volume stability at high temperature and showing an excellent resistance to thermal impacts.
2. Description of Prior Art
Conventionally it has been difficult, except for certain types of refractories, such as carbon blocks, to prepare large shapes of refractories, for example, 2 m cubic blocks, due to limitations in production equipments, such as the total available pressure of a forming press to be used, the size and strength of a mold, as well as limitations in material properties and nature, such as crackings or deformations of refractory bricks due to their expansion and contraction during their firing process or during their services at largely varying temperatures.
Meanwhile, extensive studies have been made for many years on construction of various ovens and furnaces with unshaped refractories, such as by casting installation of castable refractories and pneumatic ramming of plastic refractories for obtaining large unit shapes. However, all refractories products obtained by these prior arts show a high porosity amounting to 15% or larger. Therefore, their strength during actual services is low and their structure is low in density. These prior arts have a further disadvantage that the inter-granular vacancy in the casting or rammed shapes is increased, hence their bonding strength is lowered, because the castable refractories are given excessive water to render the casting workability easy, or plastic material, such as raw clays, are added to the plastic refractories to provide sufficient plasticity.
Further, in the case of unshaped refractories, relatively large amounts of organic and inorganic bonding materials are added for the purpose of obtaining required strength, and these large amounts of bonding materials provide main causes for a lowered fusion point, deterioration of corrosion resistance, and lowered alkali resistance in the resultant products.
In other words, it has been an ultimate object in production of all refractory structures to obtain a unitary large shape having a dense structure and free from crackings caused by non-uniform distribution of stress even under repeated services exposed to large temperature changes.
Up to now, however, large shapes of refractories having a dense structure with porisity less than 15% and less susceptible to crackings and deformations and having a stability in their volume have never been obtained.